Hearth dam



April 16, 1968 c. CONE ETAL HEARTH DAM 2 Sheets-Sheet 1 Filed July 1,1966 INVENTORS: E. DUNE F. RHINKEH RE. PINNE'Y.

April 16, 1968 c. CONE ETAL 3,378,242

' HEARTH DAM Filed July 1, 1966 2 Sheets-Sheet 2 IIIHIH INVENTORS E.DUNE 13 BUNKER, 12-5. JMNEY ATTY.

United States Patent 3,378,242 HEARTH DAM Carroll Cone, Toledo, ()hio,Robert E. Pinney, Lambertville, Mich, and Franklin G. Rinlcer, Toledo,Ohio. as-

signors to Midland-Ross Corporation, Toledo, Ohio,

a corporation of Ohio Filed July 1, 1966, Ser. No. 562,245 8 Claims.(Cl. 263-7) ABSTRACT OF THE DISCLOSURE This invention relates to ahearth dam adapted to retain a refractory hearth layer that goes througha liquid phase. The hearth darn has a plurality of vertically extendingribs that are disposed about the perimeter of the hearth and a pad isattached to the top of each rib. These pads are disposed in an end toend relationship to form a retaining structure about the hearth and aredisposed at an obtuse angle relative to the top layer of the hearth.

This invention relates to apparatus to be used during the formation ofthe top layer of a refractory hearth, and more particularly to a hearthdam for retaining the top layer of an annular refractory hearth duringfabrication thereof, when the layer goes through a liquid phase.

In the construction of refractory hearths, problems often areencountered because of the different coefficients of thermal expansion(CTE) of the various materials and apparatus used during suchconstruction. This is particularly true while making the top layer of anannular rotary hearth which goes through a liquid phase when heated toformation temperatures. The problem is compounded by the fact that theliquid has to be contained in addition to the requirement ofcompensating for expansion and contraction that occurs with changes intemperature.

It is, therefore, an object of this invention to provide a novel hearthdam for use in the construction of refractory hearths.

It is another object of this invention to provide means forconstructingthe top layer of a hearth that goes through a liquid phasewhich means accommodates expansion and contraction occasioned bytemperature changes.

it is still another object of this invention to provide a hearth dammade of heat resistant alloy.

In one embodiment of this invention, the substructure of an annularrotating hearth includes a bottom layer of insulating refractory and anintermediate layer of hard castable refractory that are received by ametal housing. Circumfereutially spaced about the inside and outsidediameters of the refractory layers, are a plurality of supporting ribswhich give backing strength to the housing. Extending from the upperedges of the intermediate layer, about the inside and outside diameters,are a plurality of pads, or plates, that extend radially inwardly andoutwardly, respectively, at an angle of approximately 45 relative to thevertical. Each pad is supported by one of the ribs and the padscooperate with one another to form a hearth dam about the inside andoutside diameters of the annular hearth. The ends of the pads are shiplap to afford movement and to eliminate a spacing between the pads whenthere is limited radial movement of the hearth darn. A layer of highpurity magnesium oxide is placed on the intermediate castable refractorylayer to complete the hearth substructure. The magnesia layer extendsradially to engage the angularly extending hearth dam, but the top ofthe dam is located substantially above the upper surface of themagnesia.

For the formation of the top layer of the rotary hearth, a finelydivided iron ore with coal fines may be used as a raw material. Thehearth substructure is rotated and 3 ,3 78,242, Patented Apr. 16, 1968the furnace is brought to temperature. The raw material is added to thetop of the substructure to form the top layer, and, as it reaches atemperature in excess of 2200 F., it forms a liquid. The top layer tendsto shrink in volume as the liquid is formed, consequently, more rawmatcrial is continually added until the desired thickness is reached inthe liquid form. As the top layer is formed it moves up and down theincline while being contained by the dam. Since the pads of the dam areat an outward angle as seen by the top layer, when the layer experiencesphysical changes, it moves up and down the slope of the darn instead ofdrawing away from its retainer to form openings therebetween or pushingagainst it to exert a force thereon.

In the drawing, FIG. 1 is a vertical view in section of a rotary hearthfurnace demonstrating features of this invention.

FIG. 2 is an enlarged cross sectional view of the furnace hearth of FIG.1.

FIG. 3 is a back view of a support member of the furnace hearth takenalong the line 3-3 of FIG. 2.

FIG. 4 is a side view of the support member taken along the line 4--4 ofFIG. 3.

FIG. 5 is a longitudinal view of a dam pad taken along the line 5-5 ofFIG. 3 and FIG. 6 is a plane view of a portion. of a rotary hearth damof this invention.

Referring now to the drawing, the rotary hearth furnace 10 includes anannular hearth 12 having a bottom layer 16 of insulating refractory thatis supported on a structural member 17 and a hard castable refractorylayer 18 on top of the bottom layer, each layer being disposed in anannular metal housing 19. Heat resistant alloy ribs 14 extend about boththe inside and outside diameters of the hearth layers 12 and 16 toprovide backing strength to the housing 19. The ribs 14have inwardlyprojecting members 20 that are received between the housing 19 and themember 17 and serve as guide means to maintain the proper elevation ofthe ribs as they extend about the hearth 12.

The top of the rib 14 is inclined at an obtuse angle relative to thehearth 12, the preferred angle being approximately and has mountedthereon a dam pad 22. The dam pads 22 extend circumferentially in an endto end relationship about the inside and outside diameters of the hearth12 to form, with the ribs 14, a hearth dam 26. Each dam pad 22 hasinterdigitating ship lap ends 24 so that adjacent dam pads are able tomove relative to one another a limited distance without creating a spacetherebetween. Extending from each side of the ribs 14 is a buttress 28,each of which cooperates with an opposed buttress on an adjacent rib tolimit the minimum distance between ribs.

Disposed on the castable refractory layer 18 is a high purity magnesiumoxide layer 30 which may be either castable or prefircd shapes. The MgOlayer extends radially to engage the hearth dam 26; however, the damextends substantially above the level of the MgO layer.

Means is provided for rotating the annular hearth 12 and includes a pairof rails 32 attached to the bottom of the structural member 17 andsupported by a rotatable shaft member 34 driven by a motor 36. Aremovable refractory cover 38 is provided to be placed over the rotaryhearth 12 and the space therebetween is sealed by a conventional waterseal 40. The cover 38 and hearth 12 have annular shell members 39 and41, respectively, that extend downwardly and are received by the waterseal 40 to complete the seal between the hearth and the cover. Suitableburner means 42 are placed into the vertical wall of the refractorycover 38 and the furnace enclosure is vented by flue means 44. As iswell known in the art, the

burners are regulated so that different temperatures are maintained atvarious zones in the furnace. Thus, as the hearth is rotated, eachportion thereof experiences temperature changes.

The top layer 46 of the hearth may be formed by using as a raw materiala finely divided iron ore with about 5% by weight of coal fines admixedthereto. This raw material is placed upon the MgO layer to the top levelof the dam 26. The hearth 12 is then rotated by actuation of the motorand the burners are lit to heat the furnace 10 so that in the hottestpart thereof the raw materials experience a temperature in excess of2200 F. At these elevated temperatures, the iron ore mixture Will form aliquid and the raw material will slowly shrink to about 1 the originalthickness. As the hearth is rotated from the hot zone to the coolerzones, which may be as low as approximately 200 F., more raw material isadded to the top layer 46 as this layer goes from the liquid phase to asolid phase. The added material rotates into the hot zone to becomeliquid and shrunk, and the process is repeated until a sufficientlythick top layer 46 is obtained. Generally, six revolutions of the hearthare required to obtain a sufliciently thick top layer.

Obviously, the primary function of the heat dam 26 is to prevent the toplayer 46 from flowing away when it is in the liquid state. The hearthdam of this invention offers other advantages when used with a rotaryhearth 12. The hearth dam 26 may be made of conventional heat resistantalloy steel. Normally, this type of alloy steel would be affected by thehigh temperature, but because of the presence of the Water seal 40, heatis radiated from the dam to the water and the metal parts of the dam arekept from being damaged by the high quantity of heat.

Normally the alloy steel dam 26 and the refractory hearth 12 would notbe compatible with one another because of the difference in CTE, for therotation through different temperature zones causes the parts of thefurnace to assume different dimensions. Ordinarily, this difference inthermal expansion would lead to stresses that could cause damage andeventual destruction of the hearth.

This is particularly true of the top layer 46, which has a CTEconsiderably higher than most refractories, when the temperature of thefurnace is reduced from operating temperatures to ambient temperature.After the top layer 46 is fabricated from raw material fines that aremelted, a monolithic slab is formed that exerts tremendous force againstits retainer as the furnace is cooled to ambient temperature. This forceis particularly critical at the inside diameter of the annular hearth,for the shrinking monolithic slab tends to crush any normal supportingmeans. The hearth darn 26 of this invention not only contains the toplayer 46 as it is formed, but also withstands the stresses imposedthrough the presence of the ship lap ends 24, the angle of the dam pads22, and the buttresses 28.

The hearth dam 26 is constructed to move radially independently of thehearth while at the same time containing the top layer 46 when the sameis liquid. The ship lap ends 24 of the darn pads 22 are able to haveradial movement without a space being created between the pads throughwhich space the liquid could flow. The dam 26 is prevented fromcontracting to an extent that it would damage the hearth because of thebuttresses 28 that extend from the sides of the ribs 14. The buttresses28 are particularly useful at the inside diameter of the hearth, forthey act as rigid structural members which engage one another to preventthe top layer 46 from crushing the hearth dam 26. The ribs 14 have acertain amount of resiliency so that they are able to yield a slightamount under pressure from the top layer as the buttresses 23 hold fast.

The dam pads 22 are positioned at an angle relative to the hearthlayers. As the dam 24 and the hearth layers, particularly the top layer,experience changes in temperature, the top layer tends to run along thesu fa e o the dam, i.e. uphill and downhill instead of away or towardit. For example, when the top layer is cooled and it changes from theliquid state to the solid state, instead of pulling away from the dam,as it would from a vertically extending container, and having spaces orholes therebetween, the layer tends to slide and maintain contact withthe dam. Thus, no openings are created through which objects may fall toact as a wedge which would eventually destroy the hearth as it changesits physical dimensions due to temperature changes. When the top layer46 is heated, instead of directing a force (that results from expansion)normal to the face of the retainer, a portion of this force is divertedthrough the movement of the layer up the incline of the pads 22.

Having the dam pads 22 at an obtuse angle relative to the hearth it)also serves another purpose. The water seal 40 is used to preventatmosphere from entering the furnace and this water seal is also used tocool the hearth dam components. By having the top of the ribs 14extending over the water seal 40, these portions are able to radiateheat to the water and remain comparatively cool. The remaining portionsof the ribs 22 are able to radiate heat to the water seal 4%) because oftheir proximity to the same.

In the above preferred embodiment, the clam pads 22 have ship lap ends24. It is obvious that other ends may work equally Well, for example,tongue-in-groove. Flat ends that abut one another may also be used, foras they separate from one another during expansion, the liquid willfreeze therein due to the pads being subject to heat loss. When the damcontracts, the frozen portions would normally break away and not createserious problems.

Although the preferred embodiment of this invention has been shown anddescribed, changes and modifications can be made therein Withoutdeparting from the scope of this invention and it is understood that thepreceding description is illustrative only and not for the purpose ofrendering this invention limited to the details illustrated or describedexcept insofar as they are limited by the terms of the following claims.

We claim:

1. A hearth dam for retaining a refractory hearth top layer that goesthrough a liquid phase, the combination comprising: a plurality ofvertically extending ribs disposed about the perimeter of the hearth,said ribs having pads attached to the tops thereof, said pads beingdisposed end to end to form a retainer about the top layers and saidretainer being at an obtuse angle relative to the top layer.

2. The hearth dam of claim 1 wherein said angle is between -160.

'3. A hearth darn for retaining the top layer of an annular rotaryhearth furnace, having a refractory substructure that supports the toplayer, the combination comprising: a plurality of pads disposed in anend to end relationship about a circumference of the substructure, saidpads extending upwardly about and at an obtuse angle relative to the toplayer, means supporting said pads, and means for radiantly cooling saidpads.

4. The combination of claim 2 wherein said angle is between 120 and 5.The combination of claim 2 wherein the ends of said pads are ship lapand adjacent ends interlock.

6. A hearth dam for retaining a liquid forming top layer of an annularrotary hearth furnace having a refractory substructure that supports thetop layer, the combination comprising: a plurality of verticallyextending ribs circumferentially spaced about a diameter of thesubstructure, a plurality of pads attached to the top of said ribs in anend to end relationship and disposed about the top layer, said padsextending upwardly at an angle between 120 to 160 relative to the toplayer, means limiting the minimum diameter bound by said ribs, and meansfor radially cooling said ribs and pads.

5 7. The combination of claim 5 wherein said pads have ship lap endsthat interdigitate with one another.

8. The combination of claim 5 wherein said diameter limiting meanscomprises a plurality of buttresses that extend in an opposed, pairedrelationship from each side of a said ribs, each buttress beingoperative to engage an adjacent buttress on an adjacent rib when saidminimum diameter is assumed.

6 References Cited UNITED STATES PATENTS 2,944,805 7/1960 Nesbitt etall. 263-' 3,061,295 10/1962 Martin et a1 263--4 FREDERICK L. MATTESON,JR, Primary Examiner. JOHN J. CAMBY, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,378,242 April 16, 1968 Carroll Cone et a1.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 4, lines 60 and 62, the claim reference numeral 2" eachoccurrence,

should read 3 Column 5, lines 1 and 3, the claim reference numeral 5",

each occurrence, should read 6 Signed and sealed this 24th day of March1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER; JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

